The Flow Cytometry Facility has undergone considerable change in the last fiscal year. It has incorporated two new flow cytometers, hired and trained 3 new employees and instituted a new computer support contract for the section. All 12 IRP Laboratories have utilized the facility, using approximately 2158 hours of instrument time for single- and multi-parameter analysis and sorting. In addition, the user-operated instruments are generating an average of 30 files/day (approx. 1-2 hrs/day). The Flow Cytometry Facility has provided support to all 12 laboratories in the IRP and many non-NIAID labs, and therefore has impacted on a wide range of research projects. These include: 1) immunology: T and B cell ontogeny, effects of interleukins/biological response modifiers on lymphoid cells, B and T cell differentiation and physiology 2) virology: AIDS related research, murine leukemia viruses, murine immunodeficiency retrovirus, vaccinia, vaccina virus; 3) parasitology: defense mechanisms to parasite invasion: 4) molecular biology: study of a variety of genes transfected into cultured cells. As the reliability of the instrumentation/personnel has become established in the facility, the frequency of repeat experiments has diminished while at the same time there has been an increased in the number of new users and projects. We expect that the level of use will increase further, particularly for sorting and multiparameter analysis. This increase was anticipated and influenced the decision to purchase the FACStar Plus and analyzers.